Heat exchangers are known in which a fluid heat exchange medium flows through a plurality of tubes. The tubes typically have a rectangular cross section and are mounted with an end portion in a header plate. In use, thermal stress can cause fatigue failure in the end portion of the tubes where they are mounted in the header plate. This reduces the life and reliability of the heat exchanger.
In order to overcome this problem it has been proposed to stiffen the ends of the tubes, particularly the tubes towards the edge of the heat exchanger which are more susceptible to thermal stress. In one known method, illustrated in FIG. 1, two separate stiffeners are inserted into the upper portions of a tube 4. The stiffeners 2 are then brazed in place during production. However, it is difficult to locate the stiffeners securely so that they abut the inner surface of the tube 4 and are at the correct depth.
A stiffener for heat exchanger tubes is also discussed in EP-A-1562015. This disclosure the use of insert members that comprise two solid insert portions joined by a connecting portion. The insert portions are bent out of the plane of the connecting portion to define a space through which coolant can flow. However, because the insert portions are solid, the stiffener must have a width corresponding to the internal width of the tube. If a different tube size is required it is necessary to change the thickness of the material from which the stiffener is made, increasing tooling costs for production. Furthermore, the use of a solid material restricts the available area of the tube for fluid flow.